1. Field of the Invention
The present invention relates to a method and apparatus for determining the temperature and/or viscosity of transmission lubricant. In particular, the present invention relates to a method/apparatus, preferably at system start-up, without requiring a temperature probe, to determine the temperature and/or viscosity of lubricant in a transmission lubricant sump of a fully or partially automated transmission system.
2. Description of the Prior Art
Change gear mechanical transmissions (i.e. transmissions shifted by engaging and disengaging selected jaw clutches), both synchronized and nonsynchronized, which operate with all or many of the gears submerged in a lubricant sump are well known in the prior art. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 4,497,396; 3,221,851; 4,754,665 and 4,735,109, the disclosures of which are hereby incorporated by reference.
Automatic and partially automatic mechanical transmission systems wherein the operation of mechanical transmissions is at least partially automated, usually by means of sensors providing input signals to a central control unit (usually microprocessor based) which processes the signals in accordance with predetermined logic rules to issue command output signals to actuators, are also well known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,676,115; 4,361,060; 4,527,447; 4,576,065 and 4,595,986, the disclosures of which are hereby incorporated by reference.
It is known that in extremely cold weather situations, until the vehicle has been warmed up, the very high viscosity of transmission lubricant due to initial low temperature thereof alters the manner in which the transmission should be operated. For example, in an automated synchronized transmission, the increased drag on the gearing caused by high lubricant viscosity often makes downshifts difficult or impossible to complete and/or undesirably time-consuming, unless the manner and sequence by which the shift is commanded is altered. Examples of transmission systems wherein transmission lubricant temperature is a control input may be seen by reference to U.S. Pat. Nos. 4,566,354; 4,572,029 and 4,799,489, the disclosures of which are hereby incorporated by reference.
The prior art automated transmission systems having lubricant sump temperature inputs were not totally satisfactory as a separate temperature probe or sensor, submerged in or adjacent to the lubricant sump was required. Aside from the added device, connector, and assembly cost, complexity and increased probability of a failure, an added dedicated sump temperature sensor also requires a dedicated CPU input port and add CPU dedicated input processing capacity.